For LED lamps, different angles of emitting light and luminous efficacy are usually got through optical elements including lenses, reflective bowl currently, etc.
Lenses are the most common optical elements in LED lamps, and mainly used to focus light.
In LED lamps, if a reflective bowl is used, optical angle control can be implemented by constructing a more complex reflective curved surface, the uniformity of light mixing is also difficult to control. When forming a light spot, it's also vulnerable to defects in optical effects, such as, bright spots at the light spot center, falsely light and stray light around the light spot, etc.
Of course, light guide pillars are also used as light guide elements in certain lamps, and so far, light guide pillars are substantially plastic light guide pillars due to the manufacturing process. The guiding principle of the light guide pillars is using two kinds of mediums of different refractive indices to enable total internal reflection of light entering into a light guide pillar to occur at the boundary of the light guide pillar, thereby implementing light guiding. As such, once the light guide pillar and its external medium changed, for example there is oil pollution or contact matters on the light guide pillar, total internal reflection of light may not be achieved entirely, then part of light may emit from the side-boundary of the light guide pillar, so that there may be a certain losses in light guiding, that is, whether a light guide pillar can carry out light guiding normally significantly depends on external influences which may cause lower light guiding stability. Considering such influences, a light guide pillar should not be fixed arbitrarily, otherwise, the refractive property of the light guide pillar may be influenced. Furthermore, all the plastic optical materials have problems of low transmittance, when the light travels longer in plastic material, there may be a lower transmittance. Plastic materials also have lower heat resistance, usually around 120°. Where near the light source on the plastic light guide pillar, there may be a burning phenomenon due to the high temperature.
Of course, the solution using a light guide tube to guide light is developed now. For example, a light guide tube is used as a light guide element in a LED remote projection lamp disclosed in the Patent Application No. 201220694731.7. However, there's a trouble in manufacturing to implement the function the light reflection and guiding as the light guide tube is cone shaped.